3. The Murky, Mediocre Middle of the Milky Way

Something is eating at the black hole at the center of our galaxy. And whatever is bugging the gravity monster manifests as an utter lack of appetite.

In October, astronomers announced they'd watched a star zip around the black hole that anchors the Milky Way, all but proving the impossible-to-see object is actually there. Meanwhile, the region around the black hole is an active place, as the Chandra X-ray Observatory showed early this year.

However, the black hole is not devouring enough matter to generate the tremendous X-ray output seen with other supermassive black holes. Scientists are so far unable to fully explain the stark contrasts they've seen, this tremendous diversity in black hole behavior.

Hints emerged this year, however. A study in January suggested mergers between two black holes might serve as an on-off switch for the activity. Then observations announced in November showed two black holes involved in a pending merger. Astronomers now need to tie all this to a firm explanation of the differences between the mediocre output of our black hole and the brilliant illumination surrounding others in many distant galaxies.

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